I always remembered my mother washing her cast iron pans with dish detergent. She just didn't leave them to soak, and she always dried them right away. When I got my own household, however, the common wisdom (of the 1980s) seemed to be never to wash it; clean it instead with a grill brush, or a salt paste, or crumpled foil. That bothered me, especially since I have a stepchild with an auto-immune disease and generally low resistance. Then I cyber-met a chef/restaurateur who told me that the health inspectors in his state would shut his restaurant down if there were evidence that pans weren't being cleaned with soap and hot water. That settled the question for me. I've never had an issue after using dish detergent on seasoned cast iron. The linked article notes why washing your cast-iron with soap and water won't disturb the seasoning you've built up, since oils become polymerized with heat. Again, just don't leave it to soak or store it without drying it thoroughly. JMO.